Liposomes have been the object of many investigations due to its potential use for the microencapsulation of medicament and its application in cosmetics and in clinical application (Teschke, O.; de Souza, E. F. Langmuir 2002, 18, 6513).
A liposome is a spherical hollow vesicle comprising mainly phospholipids which consists in an hidrosoluble head and a liposoluble tail, organized in twin layers. The lipophilic tails of phospholipids contact each other forming a double layer web which is hydrophilic in its external sections and lipophilic in its internal portion, said web enclosing an aqueous internal mass.
At present liposomes are used as carriers of various substances between the external part and the internal part of the cell due to the fact that they are the most efficient carriers to introduce substances within the cells, with a broad field of applications. Some of the substances are medicaments or cosmetics and they are even used in biotechnology, in some cases for genetic therapy, to introduce gens of an organism within a different organism.
The use of these structures as carriers has the advantage that they may be programmed in order that the medicament is capable to be released during a long period of time. Furthermore, they have a natural tendency to bind to cells and tissues obtaining the highest therapeutic efficiency and minimizing unwanted side effects. Thus, the liposomes bounded to antibodies, bind to target cells easier than the soluble forms of antibodies. From the chemical point of view, they are similar to cells circulating within the blood with which they are compatible and in the other side they constitute a useful protection method for protecting labile products due to the fact that they are not affected by degradation so that they perform efficiently.
Other reported applications attributed for these structures are as follows: to target immunomodulating agents to the cells of the immune system; controlled release of medicaments against systemic type infections, to reduce the side effects of some medicaments, as well as diagnosis methods or substitutes for blood cells.
However, the use of liposomes as carriers is not limited only to the health field, as in the textile industry the microencapsulation is a new technology which permits to substitute the dispersions or emulsions of certain substances by similar fluids in which said components are dispersed within microcapsules of inert substances, which bind to the textile material by an effective system. The final properties conferred to the textile substrate originate from the type of encapsulation carried out and the release mechanism obtained. Up to now at industrial level, the production of biofunctional tissues (smart tissues) has followed an empirical development route based on the system of “trial and error”. However, this process requires an efficient physicochemical knowledge of the interactions existing at the level of fibre-microcapsule. In the contrary case, it is not possible to optimize the application technology nor to control the release of the active principle. In this sense, liposomes are being used as microencapsulating substances in industrial processes for wool dyeing (Marti, M. et al. Textile Res. J. 2001, 71(8), 678-682; Marti, M. et al. Inter. Textile Bull. 2003, 2, 60-64; Marti, M. et al. Text. Res. J. 2004, 74(11), 961-966).
These liposomal structures, with diameters comprised between 100 nm and 1 μm have the drawback that they are too large to pass through the skin in transdermal applications.
On the other side, bicelles are disc-like nano-structures composed by a long chain phospholipid located in the centre of a flat bilayer area and a short chain phospholipid located on the edges (Sanders, C. R.; Hare, B. J.; Howard, K. P.; Prestegard, J. H. Prog. NMR Spectroscopy 1994, 26, 421). The characteristic of these systems, formed only by lipids, of organizing in twin layers and its characteristic to align to a magnetic field, has permitted its ample use as patterns for webs in different investigations of the structure of webs of proteins and peptides (Sanders, C. R.; Prestegard, J. H. Biophys J. 1990, 58, 447).
Recently, it has been proposed the use of bicelles in dermatologic applications due to its small size which is sufficient to pass through the skin. These investigations have evidenced that the action of the bicelles on the skin barrier depends on different composition variables which act as permeating agents in the skin or reinforcing agents for the lipidic structures (Barbosa-Barros, L.; Barba, C.; Cócera, M.; Coderch, L.; López-Iglesias, C.; de la Maza, A.; López, O. Inter. J. Pharmaceut 2008, 352, 263). In addition to the use of bicelles for the improvement of the skin, it is now under investigation the possibility that bicelles incorporate medicaments and other bioactive compounds.
The problem which arises when working with bicelles is that they adopt different morphologies depending on the molar rate between the long chain and the short chain phospholipids; the total concentrations of phospholipids and the temperature. Thus, as an example, in conditions of a high dilution, the small disc-like bicelles are transformed into big structures, such as vesicles, layers, rod-like micelles, etc. This behaviour could hinder the application of these systems by the systemic route due to the fact that the properties of the bicelles will be affected by dilution and the damage that these structures could generate has not yet been well defined.
A method for the stabilization of the structure of the bicelles in high dilution conditions would consist in its development starting from blends of lipids conjugated to poliethylenglycol (PEG-lipids). The problem in this method is that the obtained bicelles lose some of its characteristics, as for example, the capacity to enhance its permeability.
Therefore, a problem still persists in the stabilization of the structure of bicelles in diluted environments.